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Mumps Outbreak on a University Campus — California, 2011

Mumps is a vaccine-preventable viral disease characterized by swelling of the salivary glands; serious complications (e.g., meningitis, encephalitis, orchitis, or oophoritis) can occur. On September 29, 2011, the California Department of Public Health (CDPH) confirmed by polymerase chain reaction (PCR) three cases of mumps among students recently evaluated at their university's student health services with symptoms suggestive of mumps. An investigation by CDPH, student health services, and the local health department identified 29 mumps cases. The presumed source patient was an unvaccinated student with a history of recent travel to Western Europe, where mumps is circulating. The student had mumps symptoms >28 days before the onset of symptoms among the patients confirmed on September 29. Recognizing that at least two generations of transmission had occurred before public health authorities were alerted, measles, mumps, and rubella (MMR) vaccine was provided as a control measure. This outbreak demonstrates the potential value of requiring MMR vaccination (including documentation of immunization or other evidence of immunity) before college enrollment, heightened clinical awareness, and timely reporting of suspected mumps patients to public health authorities.

On August 25, 2011, the presumed source patient, an unvaccinated male, aged 21 years, arrived at the university's student health services with fever and unilateral facial and jaw swelling. The initial diagnosis was cellulitis and antibiotics were prescribed. By day 6 after symptom onset, the patient complained of testicular pain, and mumps was suspected. He had not been vaccinated against mumps and had traveled to Western Europe during the exposure period. He was referred for mumps serological testing, but did not follow through. His illness was not reported to the local health department when mumps was suspected. Approximately 3 weeks later, a second student, the source patient's roommate, was treated at student health services for fatigue and unilateral pain and swelling of the jaw and neck. This patient, a male aged 21 years, with a history of receiving 2 doses of MMR vaccine, received a diagnosis of parotitis. Mumps serologies were drawn, and he was advised to isolate himself in his room for 5 days. Mumps immunoglobulin M (IgM) testing was negative, and immunoglobulin G testing was positive, a pattern that does not rule out acute mumps because the ability to detect IgM is poor in vaccine recipients. The local health department was not notified. When three subsequent cases of mumps were confirmed by PCR on September 29 at CDPH, an investigation was initiated.

During the outbreak period (August 25, 2011–January 7, 2012), investigators identified 29 cases that met the Council of State and Territorial Epidemiologists 2010 case definition of mumps.* The outbreak period extended from the symptom onset date of the source patient through two incubation periods after the symptom onset of the last laboratory-confirmed case. The average incubation period for mumps is 16–18 days (range: 12–25 days); thus, the timing of the first five patients indicated that at least two generations of transmission had occurred by the time public health was notified. Case-finding activities included notifying health-care providers serving the affected community, requesting PCR testing for persons with clinically compatible symptoms, and alerting adjacent local health departments to notify CDPH of suspected mumps cases.

All patients had epidemiologic links to the university: 27 (93%) were students, one was a close contact of a student, and one was a public health staff member who assisted during a mumps vaccination clinic. Among the 29 cases, 13 (45%) were laboratory confirmed by PCR, one was confirmed by the presence of mumps IgM, and the remainder were confirmed on the basis of symptoms clinically compatible with mumps together with epidemiologic links to the university (Figure). Of the epidemiologically linked cases, 11 were negative and four were not tested by PCR. All viral specimens were genotype G, the predominant mumps genotype circulating in Western Europe. Eight patients (28%), including the source patient, were students who participated in organized sports. Four of the first five patients resided in congregate housing, and 17 (59%) illnesses occurred among students living in congregate housing. Among the 29 cases, 22 (76%) mumps illnesses occurred among persons previously vaccinated with the recommended 2 doses of MMR vaccine (Table).

CDC recommendations for mumps outbreak control include defining the at-risk population and transmission setting, and rapidly identifying and vaccinating persons without presumptive evidence of immunity (1). Other recommended control measures include cough etiquette, respiratory and hand hygiene, and isolation of infectious patients for 5 days. Early in the outbreak, the university arranged alternate housing to isolate infectious patients who resided in congregate housing; however, as the number of patients increased, this became less feasible. Students were encouraged to monitor themselves for mumps symptoms and symptomatic students were encouraged to go to student health services for testing.

Initially, the disclosure of patient student medical records to public health authorities was limited by requirements of the federal Family Educational Rights and Privacy Act (FERPA).† Because student medical records are considered educational records under FERPA, the university requested that CDPH declare the mumps outbreak an emergency, thereby permitting public health review of student medical records.

Of approximately 36,000 students enrolled at the university; an estimated 9,300 reside in housing owned by, operated by, or affiliated with the university. Recognizing that at least two generations of transmission had occurred before public health authorities were alerted to this outbreak, and wanting to avert a larger outbreak, the local health department and the university, in consultation with CDPH and CDC, decided to provide MMR vaccine as a control measure. The university recommends that matriculating students receive 2 doses of MMR vaccine, but does not require proof of MMR vaccination before matriculation, making student vaccination status difficult to assess. Therefore, messages sent to the university community advised that an additional dose of MMR vaccine, irrespective of previous MMR vaccination status, was recommended for all university community members, with an emphasis on those residing in congregate housing. Beginning 1 week after the local health department was alerted, five vaccination clinics were held during a 4-week period; a total of 3,631 persons received a dose of MMR vaccine.

Editorial Note

This outbreak demonstrates that even persons who have received 2 doses of mumps vaccine might not be protected against mumps, and highlights the importance of heightened clinical awareness and timely reporting of suspected mumps cases to public health authorities (2). The effectiveness of MMR vaccine to prevent mumps has been estimated at medians of 78% (range: 49%−91%) for 1 dose and 88% (range: 66%−95%) for 2 doses (3). Despite a substantial decline in U.S. mumps cases since mumps vaccine licensure in 1967, large mumps outbreaks have occurred in recent years among vaccinated populations (4,5). The World Health Organization indicates that only 62% of countries use mumps vaccine in national programs (6). Although MMR vaccine is included in national programs in Europe, MMR vaccination rates declined in many European countries over the last decade because of vaccine safety concerns, and outbreaks of measles and mumps have occurred. Public colleges and universities in 22 states and the District of Columbia require that enrolling students provide documentation that they have received 2 doses of MMR vaccine.

Although mumps outbreaks have occurred in populations in which many persons have received 2 doses of MMR vaccine, prematriculation MMR vaccination might prevent the introduction of mumps and limit its spread if it is introduced into a university setting (5,7). In this outbreak, the suspected source patient was unvaccinated and the outbreak might have been prevented if a prematriculation requirement had been in place. Documentation of MMR vaccination also can allow public health officials to rapidly assess the mumps vaccination status of exposed students and prioritize vaccination efforts.

Outbreak management was complicated by a delay in receiving the medical records of suspect patients. FERPA limits disclosure of student medical records by stipulating that even reportable diseases cannot be disclosed to public health authorities without prior permission from the student, except in an emergency, which is not clearly defined. An interpretation of FERPA provided by the U.S. Department of Education to the University of New Mexico in 2004 clearly states these limitations.§

Recognition and prompt reporting of clinically suspected mumps, even in the absence of laboratory confirmation, facilitates early implementation of control measures and can mitigate outbreaks. Reliable identification of mumps infections can be difficult; PCR testing is preferred when testing previously vaccinated persons. Control measures for mumps are limited. Neither MMR vaccine nor immune globulin is effective as postexposure prophylaxis; however, in an outbreak setting, MMR vaccine might reduce transmission to susceptible persons not yet exposed to the mumps virus.

Even though a population might be highly vaccinated, some persons who have received 2 doses of MMR vaccine still will be susceptible. Data collected during previous mumps outbreaks on college campuses indicate that extended person-to-person contact, in combination with waning vaccine-induced immunity, might make colleges and universities high-risk settings for outbreaks, even when 2-dose MMR vaccination coverage is high (8). In addition, patients are infectious before onset of parotitis, and asymptomatic persons can transmit disease. Isolation of patients for 5 days after parotitis onset and monitoring of contacts for symptoms are primary control measures. However, even strict isolation of reported patients is unlikely to completely interrupt disease transmission. CDC has evaluated use of a third dose of MMR vaccine for mumps outbreak control during two previous mumps outbreaks in which transmission was sustained, despite high 2-dose coverage (9,10). During both outbreaks, targeted vaccination was followed by a decrease in mumps incidence among the target group. Available data are insufficient to recommend for or against the use of a third dose of MMR vaccine for mumps outbreak control. Because control measures for mumps are limited, the ability to offer a third dose of MMR vaccine might be a tool that could be used in an attempt to limit the extent of mumps outbreaks, particularly in high-risk settings.

Colleges and universities should consider implementing prematriculation immunization requirements similar to those recommended by the American College Health Association, including ensuring that students have documented receipt of 2 doses of MMR vaccine (2). Public health officials should be aware of disclosure limitations under FERPA and how these might impact communicable disease reporting requirements and timely investigation of outbreaks. Clinicians should be diligent about reporting suspected cases of mumps to local health departments, and PCR testing should be performed for vaccinated persons with suspected mumps. More data are needed regarding the effectiveness of the use of a third dose of MMR vaccine to control outbreaks.

Mumps outbreaks can occur in populations in which a large percentage of persons have received the recommended 2 doses of measles, mumps, and rubella (MMR) vaccine. Detection of outbreaks can be delayed because falsely negative serological test results might occur in vaccinated persons.

What is added by this report?

A mumps outbreak occurred at a university that did not require proof of MMR vaccination of students before enrollment. The presumed source patient was an unvaccinated student who had recently returned from Western Europe, where mumps is circulating. Among the 29 cases, 22 (76%) mumps illnesses occurred among persons previously vaccinated with the recommended 2 doses of MMR vaccine.

What are the implications for public health practice?

Because the source patient was unvaccinated, this outbreak might have been prevented if the university had a prematriculation MMR vaccination requirement in place. Accessing the medical records of students suspected and confirmed to have mumps was complicated by federal privacy protections of education records. In addition, immunization efforts initially could have been targeted to unvaccinated or undervaccinated students if prematriculation immunization records had been available. Colleges and universities should consider ensuring that matriculating students have documentation of receipt of 2 doses of MMR. Heightened clinical awareness of mumps, appropriate testing, and rapid reporting of suspected cases to public health authorities is essential for limiting outbreaks.

FIGURE. Number of mumps cases (n = 29) at a university, by week of illness onset, and mass vaccination clinics — California, 2011

* Defined as a patient associated with the university and with signs and symptoms consistent with mumps.

† Defined as detection of virus by polymerase chain reaction or by the presence of serum mumps immunoglobulin M.

Alternate Text: The figure above shows the number of mump cases (n = 29) at a university, by dates of illness onset and mass vaccination clinics in California during 2011. All patients had epidemiologic links to the university: 27 (93%) were students, one was a close contact of a student, and one was a public health staff member who assisted during a mumps vaccination clinic. Among the 29 cases, 13 (45%) were laboratory-confirmed by polymer chain reaction, one was confirmed by the presence of mumps immunoglobulin M, and the remainder were never tested or had negative test results but had symptoms clinically compatible with mumps together with epidemiologic links to the university.

TABLE. Number and percentage of mumps patients from a university, by demographic characteristics, symptoms, and vaccination status — California, 2011

Characteristic

Laboratory confirmed*

Epidemiologic link†

No.

(%)

No.

(%)

Total

14

(100)

15

(100)

Median age (yrs)

19

—

20

—

Sex

Male

9

(64)

10

(67)

Female

5

5

(33)

Symptoms

Parotitis

14

(100)

12

(80)

Orchitis§

0

(0)

4

(40)

Vaccination status¶

Unvaccinated

0

(0)

1

(7)

1 MMR dose

1

(7)

1

(7)

2 MMR doses

11

(79)

11

(73)

3 MMR doses

2

(14)

0

(0)

Unknown

0

2

(13)

Abbreviation: MMR = measles, mumps, rubella vaccine.

* Defined as detection of virus by polymerase chain reaction or by the presence of serum mumps immunoglobulin M.

† Defined as a patient associated with the university and with signs and symptoms consistent with mumps.

§ Testicular inflammation, a postpubertal complication in males; therefore, the denominator used was male patients.

¶ Vaccination status was determined by documented history of vaccination records or self-reporting.

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